Amplifier



March 3, 1942' .DI E NORGAARD WPLIFIER Filed May 13' .1940

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Nasse VOI-GE Dorald E. Nopgaard' by Mv Mlm r-ns ,Attoffey' Patented Mar. 3, 1942 AMPLIFIER Donald E. Norgaard, Cohoes, N. Y., assigner to General Electric Company, a. corporation of New York Application May 1s, 1940, serial No. 335,947

(cl. 11s- 7.1)

5 Claims.

This invention relates to amplifiers and has amplifier which transmits a voltage between two points and prevents the introduction into the' transmitted voltage of extraneous voltages which may fortuitously exist between the two points.

It is a more particular object of my invention to provide wide-band amplifying apparatus which is necessarily `connected at spaced points of a chassis or the like and in lwhich fortuitous interferring currents which flow through the chassis are prevented from affecting the voltage which is amplified through the apparatus.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference to the following drawing in which Fig. 1 illustrates apparatus embodying one form of my invention; Fig. 2 illustratesan elaboration and modification of the embodiment of Fig. 1; Fig. 3 represents a further modification of Fig. 1; and Fig. 4 illustrates a different embodiment of my invention.

Refer-ring to Fig. 1, there is illustrated a source III of alternating voltage which is transmitted through a pair of conductors II and I2 to an electron discharge amplifying device I3, which transmits amplified waves to a load device I4. One terminal of the source I is connected toa suitable ground connection I5 which serves also to carry space current passing. from the cathode I6 of thefdevice I3 through the conductor I2, to a second suitable ground connection II and to the negative terminal of a source I8 of direct potential. The positive terminal of the source I8 is connected through the load I4 to the anode I9 of the device I3, thus completing a circuit for the space current therethrough.

Waves from the source I0 which are transmitted through the conductors II and I2 appear across a resistor 20 with which the transmission line formed by these conductors is terminated. The voltage on resistor 20 is coupled to the first or control electrode 2| and cathode I6 of the device I3 by a coupling condenser 22. The control electrode 2| yis conductively connected through a resistor y2 3 and a source 24 of biasing potential to the cathode I6. The screen electrode 25 of device I3 is connected through a source 26 of potential to the cathode I6. The source 26 is suitably by-passed for high frequency current with a by-passing condenser 21,- and serves to maintain the second electrode 25 at a substantially constant positive potential with respect to the cathode I6, which potential is preferably not more positive than the minimum positive potential of the anode I9. A third control electrode orl suppressor grid" 28 is connected directly tothe cathode I6. 4

An electron discharge device provided with electrodes'such as are shown, and with means for maintaining bias potentials on the control electrodes which are uninfluenced by any alternating voltages, has an exceedingly high anode to cathode impedance. f Such a device allows a substantially constant current to pass from its yanode to its cathode, even when the potential therebetween is varied over wide ranges. The de` vice is at the same time preferably so constructed as yto be exceedingly sensitive to potential changes of the control electrode 2 I, which can be made to produce very large changes in the anode to cathode current. f

By the circuit shown it'has been provided that noise VYvoltages which may fortuitously exist between the ground points I5 and I'I cannot substantially affect the electron current which flows `through the load device I4. This is true because the circuit is so arranged that voltages existing between the points I5 and II can produce voltage changes only between the cathode and anode of the device I3 and cannot affect the potential on any control electrode thereof, and because the current flowing between the anode and cathode is substantially independent of the voltage therebetween.

The invention isat present of greatest use in the exceedingly wide band amplifiers' required in television apparatus, which are, by their nature, very sensitive to noise voltages. One such circuit in which the inventionhas been used with great success provides for the transmission of video voltages from a portable television camera by wire to an amplier in a remote xed location.

Such a system is schematically represented in Fig. 2, wherein certain parts which correspond with like parts `shown in Fig. 1 are given like reference characters. In this gure the source I0 may, for` example, represent a camera tube for translating light into a video signal. An electron discharge device 29 serves to amplify the video signal from the source I0 before transmission from the portable camera apparatus through the conductors II and I2 to an amplifier in a remote fixed position, which amplifier includes the device I3. The amplifier 29 serves to couple the video signal from the source I0 to the trans- 'v trol electrode 35 of the device 29.

missionfline formed by the conductors il and i2. The cathode of the device 29 is connected through conductor il, resistor 2o, and conductor i2 to a central point of a source 32 of unidirectional potential, whose positive terminal is connected to anode trl of the device 29. The negative terminal of the source 32 is connected through the source l@ of video signals to a first or con- A screen electrode Sti is supplied with positive potential through a resistor 37 from the positive terminal of the source 32, and is ley-passed for high frequencies to an input terminal of transmission line. I2 lwith a by-passing condenser 33. A gas for in a somewhat different manner than by providing separate sources of potential 24 and 28 as in Fig. 1. The control electrode 2| of the device I3 is supplied through a resistor 39, a second resistor 40, and a wire 4I, which, parallel with the conductors II and I2, leads to the portable camera apparatus and is connected to `the negative terminal of the source 32. A point lbetween the resistors 39 and 40 is by-passed to the cathode I6 through a by-passing condenser 42. A biasingvoltage is therefore supplied across the condenser 42 for the control electrode 2|, which potential is not inuenced by any voltage appearing between th'e ground points I5 and Il.

Theanode I9 `is connected -in series through a resistor 43,-an inductance 44, a resistor 45,

and a source 46 of direct potential to ground' point I1, theground point I'I-being connected to the source 45 at an intermediate point, and

. the V'positive terminal thereof being connected to the resistor 45. The junction between the screen electrode 25 and the by-passlng condenser 2l is connected through a resistor 4l to the positive terminal of the source 45. The bypassing condenser 27 should be made suillciently large so that voltage which appears between the aavaeoi as in the case of the load device M and-the source it shown in Fig. l. If the condenser it point Il and would thereby be introduced into the succeeding circuits of the signal amplifying channel. That is, theA voltage across the resistance 45 would be repeated through the following stages of amplication whose input terminals would include resistance 45 therebetween. In accordance with my invention this is avoided by connecting the condenser 48 to the ground connections Il.

For purposes of illustration, a wide-band amplier coupling is shown for transmitting voltage variations from the anode I9 of the device I3 to a further electronic amplifier device 49 which is associated with the ground point I1. This wideband amplifier circuit is described and claimed in my copending application mentioned above. The anode I9 is coupled through a coupling condenser 50 to a rst or control electrode 5I of thedevice 49. The condenser 50 is of small value so that its impedance, while low at the high frequency end ofthe transmission band. is rather high at the low frequency end. The

condenser 50 is shunted by a resistor 52, a large condenser53. and a resistor 54 in series. The Y control electrode 5I is connected through a re' sistor 55 to thenegative terminal of the source 45, so that it is maintained thereby at a suitable bias potential. By properly proportioning the size of the components 43. 44, 45, 49, 50, 52, 52, 54 and 55; the transmission characteristic of this coupling network may bemade substantially ground connections I5 and Il, and consequently f vbetween the cathode I6 of the device I9 and the ground connection I1, may be effectively absorbed by the resistor 4l andA thereby prevented from substantially affecting thepotential of the screen electrode 25. The amplifier including the devicev I3 therefore functions in substantially the same way as in theapparatus illustrated by Fig. 1,

since voltages between ground connections I5 and il can appear only between the anode and cathode of device Il. I

A point between the inductance 44 and the resistance 45 is connected through a by-passing condenser 48 to the ground connections I1. This condenser 48 is provided to smooth the direct potential from the source' 45, which usually isa source of rectied alternating current. I n addition to providing such smoothing, the condenser 48 constitutes an element of an improved wideband coupling circuit disclosed in my copendlng application for Letters Patent. s. N.- 328,045,

, i'lled April 5, 1940, for Amplifier coupling circuit,

and assigned to the\same assignee as the present application. It should be noted particularly that the condenser 48 is not connected between the cathode I5 and 'the resistor 45. but is rather fiat over a wide-band. The anode 58 of the device 49 is connected through a resistor 51, which represents any suitable load device. to the positive terminal of the source 48.

A television amplifier such as that illustrated inFig. 2 may be modified slightly so as to be capable/of transmitting and Vamplifying direct currents as well as a wide frequency band of alternating currents. An amplifier capable of transmitting directcurrent components is illustrated mFig. 3 1n which certain parts, which correspond to parts illustrated in Fig. 2, are

connected4 to the ground point I1 so that the.

. entire anode circuit of the device I3 is associated with the ground point I1 (Fig. 2) exactly given like reference characters.

In Fig. 3 the ampliiler including the device 29 is identical with that in the apparatus illustrated in Fig. 2. vA source 33 is illustrated in place of the source I0 and is one which produces a direct current component together'with a wide frequency band of alternating currents.

The conductor Il is connected to the control electrode 2| through a source 58 of bias poten- .tiall which is by-passed for high frequencies by a by-passing condenser 59. The capacity lto ground point Il ofthe source 58 and the condenser 59 must be of minimum value, for other-- wise noise voltage existing between the ground connections I5 and Il would be introduced at the control electrode 2|. This is easily accomplished. since the condenser 59 need be only a verysmall condenser and the source 58 may be a very small dry cell. 'I'he cathode I6 is connected to the wire I2 through a small resistor `8l) to introduce some degeneration into the amchanges of current therethrough.

The coupling means between the devices-l 3 and 49 is modified for the transmission of direct po'- tential by shunting the coupling condenser with a resistance 62, the grid terminal of which is connected through resistance to the negative terminal of source 46. The value of resistance 62 is equal to the sum of the resistors 52 and 54 of Fig. 2. When the components of this wide-band amplier are correctly proportioned for equal transmission over the frequency band,

the resistor 62 is of a rather large value, so that by increasing the negative bias voltage supplied f rom the source 46 through the resistor 55 to the control electrode 5I a proper bias voltage on the grid of device 49 is maintained. The increase in negative biasing potential required from the source 46 is usually small.

Even'though two stages of an amplifier are placed closely adjacent to each other on a comfmon'chassis, diiiiculties have been encountered due to random currents fortuitously existing within the chassis. prevent the introduction of voltages arising therefrom into an amplifier by using the same principle which underlies the embodiments of Figs. 1, 2 and 3. Referring to Fig. 4 there is shown a source10 of video signal voltage which is amplified through an electron discharge device 1| and a second similar device 12 and Atransmitted to a load device 13. A cathode 14 of the device 1| is connected to one point 15 on a chassisl 16 through which noise currents may flow. Cathode il of the device 12 is connected to a different point 18 on thechassis 16.

Provision has been made to 1 One terminal of the source 10 is connected to i the cathode 14 and the other terminal is coupled through a suitable coupling means such as condenser 19 to the first or control electrode 8l? of the device 1|. Bias voltage is maintained on the control electrode by its connection through a resistor 8l and a 'source-9i of bias potential to the cathode 1li.

The positive terminal of a source 82, of which an intermediate point is connected to the point 18, is connected through resistors 83 and tl and an inductance B5, all in series, to the anode @it of the device 1|. The screen electrode 81 of the device 7| is maintainedat a fixed positive potential with respect to the cathode 1t by connection through a resistor dii to the positive terminal of the source til? and by a luy-passing condenser $9 connected from electrode 81 to the cathode 'M A point between the resistors t@ and Sil is connected through a by-passing con--v denser 9@ to the cathode lll of device 12.

Anyfortuitous noise voltage which may exist in thechassis it produces currents which ow in the circuit through the condenser 95, resistor 34,

inductance 85, the anode St, and cathode 'i4 bacls to the point 15 of chassis '36. pedance of the device 1| is far higher than any other impedance in this circuit, practically the entire noise voltage appears between the anode and cathode of the device 1|, the current in the anode circuit of which device is substantially constant during changes in anode voltage over a predetermined range, so that signal voltage across the inductance 85 and the resistance 84 is substantially unaffected by voltage s between points 15 and 18 on the chassis.

The Vanode 86 of the device 1| is coupled through a coupling condenser 9| to a. first or control electrode 92 of the device 12. The condenser 9|, which is provided to transmit high frequencies, is-shunted byv a series circuit comprising resistor 93,a large condenser` 94, and a resistor 95, which combination acts to transmit low frequencies. The control electrode 92 is connected through a resistor 96 to the negative terminal of the source 82, which maintains the bias voltage of control electrode 92 at a proper value. By proportioningwthe constants of this coupling circuit in a manner similar to that shown in Fig. 2, the amplier can be made to have uniform response over a wide-band of frequencies. I

The condenser 90, whichonnects the anode circuit of the device 1| tothe cathode circuit of the succeeding device 12, forms a circuit for noise voltage passing through device 1|. The device 1|, which has the characteristic that the anode currentliiowing therethrough remains substantially unaffected'by any change in voltage in the anode circuit, prevents introduction of the noise voltage into the signal transmitted through the devices 1| and 12. The bias voltage for the respective control electrodes must be supplied from a source so connected that noise voltage cannot appear on the control electrode. However, it is clearly seen that provision for bias voltages for these electrodes is not diflicult with the circuit arrangements shown.

It will be apparent to those skilled in the art that the circuits I have shown and described may be rearranged in many ways, while still conflning the noise voltages to a path including the space between the anode and cathode of a suitable electron discharge device, the impedance oi' which is so high that the current through itis not affected by such voltages. Although I have illustrated such discharge devices as multigrid tubes, it is quite feasible to utilize triodes of high anode impedance in carrying out my invention.

While I have shown a particularembodiment of my invention, it will. of course, be understood that I donut wish to be iimitedthereto, since different modifications may be made both in the circuit arrangement and instrumentalities em- Since the imployed, and I aim by the appended claims to cover any such modifications as fall within'the true spiritl and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. In combination, an electron discharge device having an anode, a cathode, and a control electrode, a circuit therefor requiring spaced ground points between which undesired voltage may exist, means for connecting said control electrode to ground only at one of said points,

said means including a signal source, means connecting said cathode to ground only at said one point, means connecting said anode to ground only at another of said points, said cathode connecting means having substantial impedance at the frequency of signals from said source whereby said undesired voltage may appear between said cathode and said one ground point, the im` pedance between said anode and cathode having ahigh value such that the current therein and the voltage on said control electrode is substantially unaffected by said undesired voltage, by reason of the fact that said undesired voltage between said ground pointscan appear only between said anode and cathode, and an output deY vice responsive to said current.

2. In combinati n, an electron discharge device having an anode, a cathode, and a control electrode, a signal source at a remote point, conduct/ors connecting said signal source between said control electrode and said cathode, said source and said device requiring spaced ground from said sourceV whereby said undesired voltage may appear on said co-ntrol electrode, said anode and cathode having impedance therebetween of high value such that the current therethrough is substantially unaffected by changing voltage therebetween, whereby vsaid undesired voltage does not afiectsaid current or the voltage on said control electrode, and an output device responsive to said current.

3. In combination, a television camera and a remotely situated amplier for video signals produced thereby, said camera and said amplifier requiring spaced ground points between which undesired voltage may exist, and said ampliier comprising an electron discharge device having an anode, a cathode, anda control electrode, a pair of conductors connected from said camera to said cathode and control electrode to impress video signals therebetween, means connecting' said cathode and its conductor toground only through the ground point at said camera, means connecting said anode to ground' only through another of said ground points, said control electrode being connected to ground only at the ground point at said camera, the impedance ofl said. conductors being substantial at the frequency of said video signals whereby said undesired voltage .may be impressed on said control the current therethrough and the voltage on said control electrode is substantially' unaiected by said undesired voltage, and an output device responsive to said current.

4, In combination, an electron discharge de vice having an anode, a cathode, and a control electrode, a signal source, said source and said device .having separated ground .connections which may have undesired voltage therebetween,

.circuits connected with said device including conductors connecting said source between said cathode and said control electrode and a circuit passing through said separated ground connections, said cathode being connected to ground only through the ground connection at said source, said conductors having substantial impedance whereby undesired currentvariations produced in said conductors by said undesired voltage produce undesired voltage on said control electrode, pand means connecting every circuit connected with' said device and passing through said separated ground connections through the anode and cath-l ode of said device, said device having a characteristic such that current flowing -in its anode and cathode is substantially unaffected by said undesired voltage impressed therebetwemwhereby said undesired voltage does not appear on said l of said one conductor so arranged that alternatelectrode, said anode and cathode having impedance therebetween of high value such that ing currentilowing in said one conductor must flow through the anode and cathode of said device, 'said control electrode being connected to ground only'at said ground point through said source, an output circuit connected between said anode and a second ground point and providing the only ground connection for said anode, whereby undesired voltage existing 'between said ground points may aiect the value of said alterhating current undesirably, the impedance between said anode and cathode being 4oi high value such that the value of said current is not undesirably affected by 'said undesired voltage.

DONALD E. NORGAARD. 

